Dark Mode

Adding dark mode to your Astro project.

Create an inline theme script

---
import "../styles/globals.css";
---

<script is:inline>
  const getThemePreference = () => {
    if (typeof localStorage !== "undefined" && localStorage.getItem("theme")) {
      return localStorage.getItem("theme");
    }
    return window.matchMedia("(prefers-color-scheme: dark)").matches
      ? "dark"
      : "light";
  };
  const isDark = getThemePreference() === "dark";
  document.documentElement.classList[isDark ? "add" : "remove"]("dark");

  if (typeof localStorage !== "undefined") {
    const observer = new MutationObserver(() => {
      const isDark = document.documentElement.classList.contains("dark");
      localStorage.setItem("theme", isDark ? "dark" : "light");
    });
    observer.observe(document.documentElement, {
      attributes: true,
      attributeFilter: ["class"],
    });
  }
</script>

<html lang="en">
  <body>
    <h1>Astro</h1>
  </body>
</html>

Add a mode toggle

import * as React from "react";
import { Moon, Sun } from "lucide-react";

import { Button } from "@/components/ui/button";
import {
  DropdownMenu,
  DropdownMenuContent,
  DropdownMenuItem,
  DropdownMenuTrigger,
} from "@/components/ui/dropdown-menu";

export function ModeToggle() {
  const [theme, setThemeState] = React.useState<
    "theme-light" | "dark" | "system"
  >("theme-light");

  React.useEffect(() => {
    const isDarkMode = document.documentElement.classList.contains("dark");
    setThemeState(isDarkMode ? "dark" : "theme-light");
  }, []);

  React.useEffect(() => {
    const isDark =
      theme === "dark" ||
      (theme === "system" &&
        window.matchMedia("(prefers-color-scheme: dark)").matches);
    document.documentElement.classList[isDark ? "add" : "remove"]("dark");
  }, [theme]);

  return (
    <DropdownMenu>
      <DropdownMenuTrigger asChild>
        <Button variant="outline" size="icon">
          <Sun className="h-[1.2rem] w-[1.2rem] scale-100 rotate-0 transition-all dark:scale-0 dark:-rotate-90" />
          <Moon className="absolute h-[1.2rem] w-[1.2rem] scale-0 rotate-90 transition-all dark:scale-100 dark:rotate-0" />
          <span className="sr-only">Toggle theme</span>
        </Button>
      </DropdownMenuTrigger>
      <DropdownMenuContent align="end">
        <DropdownMenuItem onClick={() => setThemeState("theme-light")}>
          Light
        </DropdownMenuItem>
        <DropdownMenuItem onClick={() => setThemeState("dark")}>
          Dark
        </DropdownMenuItem>
        <DropdownMenuItem onClick={() => setThemeState("system")}>
          System
        </DropdownMenuItem>
      </DropdownMenuContent>
    </DropdownMenu>
  );
}

Display the mode toggle

Place a mode toggle on your site to toggle between light and dark mode.

---
import "../styles/globals.css";
import { ModeToggle } from "@/components/ModeToggle";
---

<!-- Inline script -->
<html lang="en">
  <body>
    <h1>Astro</h1>
    <ModeToggle client:load />
  </body>
</html>